The present invention relates to a system for pumping fluid at a constant, high pressure into a reaction vessel or other container, particularly a vessel used in the explosive comminution of coal into fine particles.
Explosive comminution of coal may be accomplished by raising the pressure and temperature of a coal-fluid slurry, preferably coal-water, then suddenly lowering the pressure of the slurry, for example by forcing the slurry through a pressure reducing orifice. The pressure reduction effects a rapid expansion of the fluid in the coal particles, causing the coal to shatter or explode into smaller sized particles.
Coal slurries, however, are difficult to handle particularly at high temperatures, due to the tendency of coal particles in the slurry to agglomerate. Such agglomeration can partially or fully plug the pressure reducing orifice thereby producing sudden and severe pressure increases within the comminution system. Continued pumping of a slurry in a plugged system can ultimately cause damage to the system, for example, by causing rupture of pipes or vessels, or destruction of pumps. However, if the feed pump for the comminution system is designed to deliver the slurry at a constant pressure, then the delivery rate of the slurry is inherently adjusted, decreased or stopped so as to maintain a safe pressure.
Conventional constant pressure feed pumps utilize a feed back loop around the pump. The loop includes a pressure actuated valve that may be actuated to divert the pumped fluid into the feedback loop whenever a threshold pressure is sensed at the pump head. However, when an abrasive slurry, such as a coal slurry, flows through the feedback loop, the control valve is severely abraded making it unsuitable for use in a relatively short time. Such a bypass system may also cause undesirable rapid heating of the fluid being pumped in the feedback loop as the pump continuously circulates the fluid through the loop.
The present invention was devised to overcome certain problems discovered in these conventional systems. The invention provides a system for delivering fluids, particularly abrasive slurries such as a slurry of coal and water, at a constant high pressure in a manner which protects the integrity of the pumping system and the vessel or device which receives the slurry.